Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?

Can a 50 Hz, 220 VAC transformer work on 40 Hz, 180VAC?

Yes it probably can - the initial worry is saturation problems due to operating at the lower frequency but, with the voltage dropping to 180 V at 40 Hz, this produces virtually the same magnetization current as 220 V at 50 Hz.

Strictly speaking, if the transformer is nominally rated for 220 V at 50 Hz, you should run it at a nominal voltage of 176 V at 40 Hz.